#递归
'''
sum = 1;
x = 1;
def jieCheng(num):
    global x
    global sum
    x += 1
    sum = sum * x
    if(x == num):
        return print(sum)
    else:
        return jieCheng(num)
'''
def jieCheng(num):
    if num == 1:
        return 1
    else:
        return num * jieCheng(num -1)
number = int(input("请输入一个数："))
print(jieCheng(number))